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Heat Acclimation Training

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[[File:2013 Badwater.jpg|right|thumb|500px|I've done quite a bit of [[Running in the Heat]], from North Carolina's brutal summers, to winning the [[2010 Keys 100]] or pacing Chris Moon at the [[2013 Pacing Badwater 135| Badwater 135]].]]
Heat acclimation training can improve performance in hot and cold conditions. It also helps protect against heat injury and is particularly important when training for spring races. However, heat adaptation training can be dangerous and care must be taken to avoid injury or death.
Training for a spring race requires extra caution as you will have been training through the winter and be unprepared for warm conditions. While a spring race may be cool, there is also a risk of conditions that are warm enough (above 40f) to impair performance (see [Impact of Heat on Marathon Performance] for more details). Heat acclimation training, sometimes called heat adaptation training, can prepare you for these warmer conditions. This type of training is also valuable if you are traveling to a warmer climate for a race, or if you are training in the cool part of the day for a race in the warmer times. In addition, heat acclimation can improve cold weather performance. One study<ref name="performance"/> showed that heat acclimation improved performance in the cold by 6% and by 8% in heat.
* [[Nausea]] or vomiting. These symptoms can occur before true heatstroke, as running makes digestion harder.
* Weakness. An unusual muscular weakness could be due to low blood sugar, but elevated core temperature also creates weakness.
* Headache. This can also be caused by dehydration, or low blood sugar. Having had headaches from each of the three causes, I have found the type of headache is different. My limited experience is that a headache cased caused by heat is particularly painful and intense.
* Dizziness or confusion. This is a serious symptom that suggests either extremely low blood sugar or heatstroke.
* Panting. My personal experience is that when my core temperature rises, I start to breathe more rapidly. The panting can occur at rest in a sauna, or during exercise where my breathing rate is far deeper and faster than would be typical for the exercise intensity. This panting may be a reflect that attempts to cool the body in the same way as a panting dog. I find this is the first warning of problems and a sign that I have to reduce the heat stress rapidly.
If you have any doubts, stop and check your temperature. Never do [[High Intensity Interval Training]] as part of heat acclimation; the intense work can spike your core temperature too high too quickly for you to recover.
=Practical Heat Training=
* Use gradually increasing periods from 30 to 100 minutes over 10 to 14 days<ref name="Shapiro"/>
* Acclimation is fully developed after 7 to 14 days<ref name="Armstrong-1991"/>, but up to 75% of acclimation is reached after 5 days <ref name="Shapiro"/>.
* Reduce your training load to compensate for the added stress of the heat. The heat can make you far more tiered tired than you would expect.
* Consider alternating heat acclimation training and cooler training to preserve intensity<ref name="Noakes"/>
* Training in a warmer environment is ideal, but creating a microclimate (see Heat Suit below) by overdressing also works<ref name="Noakes"/>
* Exercise in heat produces better acclimation than passive heat<ref name="ismj"/>, but passive heat (sauna) following exercise can also be quite effective<ref name="postsauna"/>.
* Maintain hydration levels, as dehydration may impair key adaptations, such as increased sweat rate<ref name="TraversNichols2020"/>.
* Once gained, heat adaptation can be maintained for at least a month by training in the heat every five days<ref name="PryorPryor2019"/>. Without continued heat exposure, it's estimated that 2.5% of adaptation is lost each day<ref name="DaanenRacinais2017"/>.
=Fellrnr Heat Suit=
This 'heat suit' will allow for heat training even in quite cool conditions.
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This heat suit works by preventing the body cooling itself, so it increases the risk of heat stroke. If you overheat wearing this heat suit, you may not cool off after you collapse. Please be careful taking this approach, and start off with very low intensity exercise. Build up the duration and intensity very gradually, and monitor for warning signs. Please be careful, as I've had some close calls using this technique and it is dangerous. See "Symptoms of Heat Stroke" above.
* On return to a cool climate, acclimation lasts for about a week, then decays<ref name="Armstrong-1991"/>
* People who have always lived in hot climates are believed to have superior adaptation<ref name="Noakes"/>
* A sauna will produce similar heart rate and cardiac stress as 60-100w of exercise<ref name="KetelhutKetelhut2019"/>. My experience matches that estimate for heart rate, though my respiration tends to be much higher as my body attempts to pant to cool off.
=See Also=
* Running calculators
<ref name="performance"> S. Lorenzo, JR. Halliwill, MN. Sawka, CT. Minson, Heat acclimation improves exercise performance., J Appl Physiol (1985), volume 109, issue 4, pages 1140-7, Oct 2010, doi [ 10.1152/japplphysiol.00495.2010], PMID [ 20724560]</ref>
<ref name="NielsenHales1993">B Nielsen, J R Hales, S Strange, N J Christensen, J Warberg, B Saltin, Human circulatory and thermoregulatory adaptations with heat acclimation and exercise in a hot, dry environment., The Journal of Physiology, volume 460, issue 1, 1993, pages 467–485, ISSN [ 00223751], doi [ 10.1113/jphysiol.1993.sp019482]</ref>
<ref name="KetelhutKetelhut2019">S. Ketelhut, R.G. Ketelhut, The blood pressure and heart rate during sauna bath correspond to cardiac responses during submaximal dynamic exercise, Complementary Therapies in Medicine, volume 44, 2019, pages 218–222, ISSN [ 09652299], doi [ 10.1016/j.ctim.2019.05.002]</ref>
<ref name="PryorPryor2019">J. Luke Pryor, Riana R. Pryor, Lesley W. Vandermark, Elizabeth L. Adams, Rachel M. VanScoy, Douglas J. Casa, Larry E. Armstrong, Elaine C. Lee, Lindsay J. DiStefano, Jeffrey M. Anderson, Carl M. Maresh, Intermittent exercise-heat exposures and intense physical activity sustain heat acclimation adaptations, Journal of Science and Medicine in Sport, volume 22, issue 1, 2019, pages 117–122, ISSN [ 14402440], doi [ 10.1016/j.jsams.2018.06.009]</ref>
<ref name="TraversNichols2020">Gavin Travers, David Nichols, Nathan Riding, José González-Alonso, Julien D. Périard, Heat Acclimation with Controlled Heart Rate, Medicine & Science in Sports & Exercise, 2020, pages 1, ISSN [ 0195-9131], doi [ 10.1249/MSS.0000000000002320]</ref>
<ref name="DaanenRacinais2017">Hein A. M. Daanen, Sebastien Racinais, Julien D. Périard, Heat Acclimation Decay and Re-Induction: A Systematic Review and Meta-Analysis, Sports Medicine, volume 48, issue 2, 2017, pages 409–430, ISSN [ 0112-1642], doi [ 10.1007/s40279-017-0808-x]</ref>

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